1. Field of the Invention
The present invention relates generally to electronic packaging, and more particularly to thin/low profile surface mount packaging having multiple, aligned emitters for application versatility.
2. Description of the Related Art
Light emitting diodes (LEDs) are solid state devices that convert electric energy to light, and generally comprise one or more active layers of semiconductor material sandwiched between oppositely doped layers. When a bias is applied across the doped layers, holes and electrons are injected into the active layer where they recombine to generate light. Light is emitted from the active layer and from all surfaces of the LED.
In recent years, there have been dramatic improvements in LED technology such that LEDs with increased brightness and color fidelity, smaller footprints, and overall improved emitting efficiency have been introduced. LEDs also have an increased operation lifetime compared to other emitters. For example, the operational lifetime of an LED can be over 50,000 hours, while the operational lifetime of an incandescent bulb is approximately 2,000 hours. LEDs can also be more robust than other light sources while consuming less power. For these and other reasons, LEDs are becoming more popular and are now being used in more and more applications that have traditionally been the realm of incandescent, fluorescent, halogen and other emitters.
Due at least in part to these improved LEDs and improved image processing technology, LEDs can be used as the light source for a variety of display types. In order to use LED chips in these types of applications, it is known in the art to enclose one or more LED chips in a package to provide environmental and/or mechanical protection, color selection, light focusing and the like. An LED package also includes electrical leads, contacts or traces for electrically connecting the LED package to an external circuit. The LED packages are commonly mounted on a printed circuit board (PCB).
Different LED packages can be used as the light source for displays, both big and small. Large screen LED-based displays are becoming more common in many indoor and outdoor locations, while smaller screen LED-based displays such as televisions, gaming machines, and computer monitors are becoming more common in many indoor locations such as homes and businesses. These LED-based displays can comprise thousands of “pixels” or “pixel modules”, each of which can contain a plurality of LEDs. The pixel modules can use high efficiency and high brightness LEDs that allow the displays to be visible from various distances and in a variety of environmental lighting conditions. The pixel modules can have as few as three or four LEDs that allow the pixel to emit many different colors of light from combinations of red, green, blue, and/or sometimes yellow light.
Most conventional LED based displays are controlled by a computer system that accepts an incoming signal (e.g. TV signal), and based on the particular color needed at the pixel module to form the overall display image, the computer system determines which LED(s) in each of the pixel modules is to emit light and how brightly. A power system can also be included that provides power to each of the pixel modules; the power to each of the LEDs can be modulated so light is emitted at the desired brightness. Conductors are provided to apply the appropriate power signal to each of the LEDs in the pixel modules.
Viewers are often not directly in front of an LED-based display when it is viewed. Both indoor and outdoor displays are viewable across a substantial range of off-axis angles, such as up to 145° or even greater. Depending on where the viewer is located, the horizontal and/or vertical viewing angle can be different. Furthermore, when a person is moving by an LED display, it is viewed at many different angles. Typical LED displays with peak emissions near the center can experience a drop-off in emission intensity at different angles. The far field pattern (FFP) for the different LED packages in each of the pixel modules can also be different such that the LED display can experience image quality variations when viewed from different angles.
Thin, flat panel displays are becoming more common in both indoor and outdoor applications. As the popularity of flat displays rises, LED packages incorporated into such displays have necessarily become thinner/lower profile. The thin/low profile packages are expected to be robust such that they maintain their structural integrity during manufacture and use, but the integrity of such packages can become compromised. For example, in current thin/low profile packages in the art, the package structures can become deformed during the reflow process. Furthermore, current thin/low profile packages may experience separation between the package casing and the leads/lead frame during manufacture and use.
Additionally, as emitter packages become smaller and lower profile, the amount of space available for emitting components (such as LEDs) on the electrically conductive portions of the packages is at a premium. The smaller packages may also comprise dimensions which prevent them from corresponding with mounting portions of conventional PCBs or other suitable mechanical/electrical supports.